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| Noisy and unstable 2C22/7193 |
Moving closer to civilization, this lovely sounding triode used as a voltage gain stage in my SE2A3 mono integrated amp had stability issues due to RFI.
Since I persist in using these antediluvian devices, I had to find a solution.
A 150 ohm 1/2W CC resistor with the leads cut short soldered in series with the grid cap (insulate with heat shrink tubing) >> shielded cable terminated by an RCA plug (shield connected only at the RCA jack side) >> RCA jack (barrel grounded to chassis) solved the stability issue.
A 150 ohm 1/2W CC resistor with the leads cut short soldered in series with the grid cap (insulate with heat shrink tubing) >> shielded cable terminated by an RCA plug (shield connected only at the RCA jack side) >> RCA jack (barrel grounded to chassis) solved the stability issue.
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| A well behaved 2C22/7193 |
Are you using shielded cable to the grid? When using very high transconductance tubes like the 5842/417 or 437 grid stoppers are pretty much mandatory, 417/5842 has 4 grid pins, have to use one on each pin....
ReplyDeleteRoscoe
Yes, shielded cable was good enough before. Now the grid resistor was the only cure. Maybe it's my proximity to more airwaves?
DeleteJE